Transmission line



Oct. 22, 1957 D. BLITZ TRANSMISSION LINE Filed March s. 1954 Daniel Blitz zzvmvrox.

ATTORNEY United States Patent TRANSMISSION LINE Daniel Blitz, Boston, Mass., assignor to Sanders Associates, Incorporated, Nashua, N. H., a corporation of Massachusetts Application March 5, 1954, Serial No. 414,293

6 Claims. (Cl. 33384) The present invention relates to transmission lines. More particularly, the invention relates to transmission lines such as are used in association with high frequency electronic devices.

In modern shortwave techniques transmission lines in a form familiarly known as wave guides are widely used. Because of the construction these wave guides occupy a large volume of space and are heavy and expensive to manufacture.

As an alternative to such wave guides, various configurations have been proposed that may be more readily reconciled with the use of printed circuits and etched circuit techniques.

In the prior art, a so-called sandwic line has been proposed in which a pair of ground plane, outer conductors have sandwiched between them an inner conductor of lesser width. These sandwich lines are typically prepared from a pair of copper-foil-clad, T eflon- Fiberglas laminates. The transmission line is formed from two lamination sections one of which is composed from an elongated, Teflon-Fiberglas insulating panel hav ing a ground conductor aifixed to one flat side and an etched inner conductor affixed to the opposite, flat side. The other section has only an insulating panel and a ground conductor. The two transmission line sections are typically assembled together with the inner conductor sandwiched between the two outer conductors by means of rivets or clamps. Such a line is subject to asymmetries in the ground-conductor-to-inner conductor spacings due to flexure or vibration. As is well known in the prior art, the spacing from the inner conductor to each of the outer conductors must be equal for the line to remain balanced and to maintain a constant characteristic impedance. When the spacing from the inner conductor to either of the outer conductors is unbalanced or asymmetrical due, for example, to separations between the above-mentioned lamination sections, the characteristic impedance is radically changed and causes reflections and resultant increased insertion losses.

In the transmission line of the present invention, the lamination sections are each composed of an outer conductor, an insulating panel and an inner conductor. When used as a unitary, composite, transmission line, the two sections are assembled together with the, inner conductors connected together. By constructing a sandwich transmission line in this manner, the inner conductor-to-outer conductor spacings are preserved and maintained constant regardless of limited relative motion between the inner conductors and, hence, between lamination sections.

It is, therefore, an object of the invention to provide an improved transmission line in which relative movement of its parts has substantially no effect on the propagation characteristics of the line.

A further object of the invention is to provide an improved transmission line which is economical to fabricate and light in weight.

Yet another object of the invention is to provide an 2 improved transmission line exhibiting a high degree of reliability and reproducibility.

Other and further objects of the invention will be apparent from the following description of a typical embodiment thereof, taken in connection with the accompanying drawings.

In accordance with this invention there is provided a composite, unitary high frequency electric transmission line structure susceptible to flexure of its parts comprising a pair of elongated outer conductors providing electrical ground planes. A pair of elongated inner conductors is held with the conductors adjacent each other and in electrical contact between and in spaced insulated relation to the outer conductors, to operate electrically as a single conductor, while permitting variation of the spacing between the inner conductors without substantially disturbing the electric energy propagation efficiency of the transmission line. The inner conductors are of lesser width than the outer conductors. One of the inner conductors may be of lesser width than the other inner conductor to permit limited relative transverse motion of the inner conductors without disturbing the impedance characteristics of the line. Means are provided for securing the conductors in their relative positions in the line.

In the accompanying drawings:

Fig. 1 is a three-dimensional view illustrating an embodiment of this invention;

Fig. 2 is a view illustrating the connection of a source of high frequency power to a transmission line embodying this invention; and

Fig. 3 is a cross-sectional view of another embodiment of the invention.

Referring now in more detail to the drawings, an outer conductor 1 is attached to the upper surface of a dielectric 2 with a suitable cement. A11 inner conductor 3 is attached to the under surface of the dielectric 2. An inner conductor 4 is attached to the upper surface of a dielectric 5 and an outer conductor 6 is attached to its under surface.

A generator 7 may be connected to the transmission line embodying this invention as shown in Fig. 2. One side of the generator 7 may be connected to ground and to the outer conductors 1 and 6. The other side of generator 7 may be connected to the inner conductors 3 and 4.

Theoretically, a transmission line composed of inner conductors of finite width and spaced between outer conductors that are parallel and of infinite width would permit no radiation of high frequency energy from the line. By selecting the width of the outer conductors to be sufliciently greater than that of the inner conductors, a relatively low radiation loss is obtained for the transmission line.

By forming the transmission line in two sections, the one comprising outer conductor 1, dielectric 2, and inner conductor 3 and the other comprising outer conductor 6, dielectric 5 and inner conductor 4, the two sections may be permitted transversely to move relative to each other a limited amount in the direction indicated at 8. The effect of the present invention is substantially to preserve the impedance characteristics of the line in the presence of such motion.

A relatively small phase shift may be introduced by the transverse relative movement of a section of line; for example, less than 30 degrees. Ordinarily, such a shift is unobjectionable and it sometimes may be utilized. Another embodiment of the invention permits an extra degree of limited transverse motion between two sections of the transmission line, in the direction as indicated at 9. By providing the inner conductor 10 :or introducing excessiveradiation loss, a

Wider than inner conductor 11, limited movement between the two line sections is permitted, essentially without disturbing the impedance characteristics of the line Since the physical parameters of'the transmissionline as described above may be varied without substantially bodiment illustrated without departing from the spirit of the invention. It will be understood, therefore, that all those changes and modifications as fall fairly within the scope of the present invention, as defined in the appended claims, are to be considered as a part of the present invention. 7

What is claimed is: a V

'1. A composite, unitary, high-frequency, electric, transmission line structure susceptible to flexure of its parts, comprising: a pair of elongated outer conductors providing electrical ground planes; a pair of elongated inner conductors, held adjacent each other, and in electrical contact between and in spaced insulated relation to Said outer conductors, to operate electrically as a single conductor, while permitting variation of'the spacing between said inner conductors Without substantially disturbing the electric energy propagation efiiciency of said transmission line; and means securing said conductors in their relative positions. 7 g 2. A composite, unitary, high-frequency, electric, transmission line susceptible to flexure of its parts, comprising: a pair of parallel, outer conductors providing electrical ground planes; a pair of inner conductors so connected as to operate electrically as a single conductor to permit variations of the spacing between the inner. conductors without substantially disturbing the propagation efficiency of said transmission line, said inner conductors being narrower than said outer conductors; and means'securing said conductors in their relative positions to confine propagated electric energy'within the limits of said outer conductors.

3, A composite, unitary, high-frequency, electric, transmission line structure susceptible to fiexure of its parts, comprising: a pair of elongated outer conductors providing electrical ground planes; a pair of inner conductors, one of said inner conductors being narrower than the otherof said inner conductors, said inner conductors being connected together to operate electrically as .a single conductor, while permitting variation of the spacing between said inner conductors without substantially disturbing the electric energy propagation elficiency of said transmission line; and means securing said conductors intheir relative positions. 7

4. A composite, unitary, high-frequency, transmission line structure susceptible to flexure of its parts, comprising: a first pair of elongated parallel conductors; dielectric material binding said conductors in insulated spaced relation; a second pair of elongated electric; 1

conductors; and dielectric material binding the .conductors of said second pair together in insulated spaced re-' lation, said first and second conductor pairs being held parallel to and adjacent each other to provide a pair of outer conductors providing substantially infinite electrical ground planes and a pair of adjacent inner conductors, said inner conductors being connected to operate elec trically as .a single conductor, while permitting variation of the spacing between said inner conductors without substantially disturbing the propagation elficiency of said transmission line and enabling said line to operate as a unitary guide for high, frequency electric energy Within the confines of said outer conductors.

5. A composite, unitary, high-frequency, electric,

transmission'line structure susceptible to fleXure of its parts, comprising: a first pair of elongated parallelconductors; dielectric material binding said conductors in insulated spaced relation; a second pair of elongated conductors; and dielectric material binding the conductors of said second pair together in insulated spaced relation, said first and second conductor pairsbeing held parallel to and adjacent each other to provide apair of outer con ductors providing two substantially infinite electrical ground planes and a pair of adjacent inner conductors, said inner conductors being so connected as to operate electrically as a single conductor while permitting lim- 'ited transverse movement between said inner conductors without substantially disturbing the propagation efliciency of said line. i V a 6, A composite, unitary, high-frequency, electric transmission line structure susceptible to flexureof its pang-comprising: a first lamination section having an elongated insulator panel, an elongated, planar outer conductor afixed to o'ne side of said panel an elon- V gated, planar, inner conductor, ;narrower than said outer conductor, afiixed to the opposite side of said panel;

a second lamination section having an elongated insulator panel, an elongated,: planar, outer conductor af-V gether as a single conductor, whereby the inner-conductor-to-outer-conductor spacings are maintained constant with variations of the spacing between said sections, thereby maintaining the propagation characteristics of said transmission line substantially constant and enabling said line to operate as a unitary guide for high-frequency, electric energy within the confinesof said outer conductors. I a

References Cited in the file of this patent I FOREIGN PATENTS 541,380

Great Britain Nov. 25, 1941 570,087 Great Britain ,June 21,- 1945 601,514

Great Britain May 7, 1948 OTHER R FERENCES Radio-Electronic Engineering; September 1951; pp;

16 and 31V. 

